The use of medicine injection apparatuses such as injectors typically involves sucking-in medicine from a vial. A vial is a medicine storage container in which medicine can be preserved for an extended time in a liquid or freeze-dried state. An opening part of the vial is normally sealed with a rubber stopper having a thickness of 3 to 5 mm. The rubber stopper is designed so that it does not permit leakage of the medicine therethrough, even when it is repeatedly pierced by a needle tube. Therefore, most of vaccines used often for group vaccination are sucked in from vials.
A common method of sucking medicine from a vial into a syringe involves first connecting a needle hub fitted with a suction needle tube of about 22 gauge to the syringe. Next, the suction needle tube is used to pierce the vial, and the liquid medicine is sucked into the syringe. Thereafter, the needle hub fitted with the suction needle tube is detached from the syringe, and a needle hub fitted with an injection needle tube is attached to the syringe. As a result, the medicine injection apparatus is in the state of being capable of injecting the medicine. After the medicine is injected (administered) by the medicine injection apparatus, some medicine is left in the needle tube, in the needle hub and in a distal portion of the syringe.
The skin is composed of three portions: the epidermis, the dermis, and the subcutaneous tissue. The epidermis is a layer of about 50 to 200 μm ranging from the surface of the skin, and the dermis is a layer of about 1.5 to 3.5 mm continuing from the epidermis. An influenza vaccine is ordinarily administered in a hypodermic or intramuscular manner, and, therefore, it is injected into a lower layer part of the skin or a part deeper than the lower layer part.
To reduce doses of the influenza vaccine, administration of the vaccine while taking as a target region a skin upper layer region where a lot of immunocytes are present has been investigated. The term “skin upper layer region” used here means the epidermis and the dermis, of the skin. The dose of the vaccine administered into the skin upper layer region is about 50 to 300 μL, preferably about 100 μL. Therefore, if the amount of the medicine left in the assembly or apparatus upon injection is large, the merit of reducing the quantity of antigen obtained by administering the vaccine into the skin upper layer region is lessened.
Further, the administration of a medicine into the skin upper layer region requires a higher injection pressure, as compared with hypodermic administration. Therefore, if the amount of air left in the engaging part between the syringe and the hub is increased, the remaining air forms a pressure interference zone, whereby it may be made impossible to secure an accurate dose.
Technologies for reducing the residual amount of medicine upon injection include a technology described in Japanese Utility Model Publication No. Sho 61-28629 (hereinafter referred to as Patent Document 1). A needle base part of the injection needle described in Patent Document 1 is provided with an insertion member and a stop member. The insertion member is formed from a synthetic rubber, a synthetic resin or the like which is elastic, and is so designed as to connect the injection needle with an injection cylinder and to fill up a dead volume of an injection needle attachment mouth (tip) formed at the distal end of the injection cylinder. The stop member is fitted in the tip of the injection cylinder.
Another technology for reducing the residual amount of medicine upon injection is described in Japanese Patent Laid-open No. 2006-116217 (hereinafter referred to as Patent Document 2). The injector described in Patent Document 2 has a configuration in which an injection needle and an outer cylinder having a cylinder tip in which to insert the injection needle are separable from each other. The cylinder tip of the outer cylinder has an opening part, the diameter of which is increased along the distal direction. In this case, the injection needle inserted into the cylinder tip is fitted in and put in contact with a minimum diameter part of the cylinder tip.
In the injection needle described in Patent Document 1, the operation of fitting the insertion member into the tip of the injection cylinder is troublesome. In the case of sucking a medicine from a vial, it is necessary to both attach the suction needle to the outer cylinder and attach the injection needle. Therefore, the injection needle described in Patent Document 1 is not well suited to use where a medicine is sucked from a vial so as to be used.
The injector described in Patent Document 2 is constructed such that the opening part formed at the cylinder tip of the outer cylinder is gradually enlarged in diameter along the distal direction, which permits the injection needle to be easily relatively inserted into the cylinder tip at the time of fitting the hub part to the outer cylinder. However, the injector described in Patent Document 2 makes it necessary to insert the needle tube into the cylinder tip of the outer cylinder by a predetermined length and fit the needle tube to a minimum diameter part of the cylinder tip. Thus, the base end (terminal end) of the needle tube must be precisely positioned in relation to the hub part fitted to the outer cylinder.
In the case of taper fitting between the injection cylinder and the injection needle, a dead volume would be generated between a distal end portion of the tip of the injection cylinder and the needle tube.